U.S. patent number 5,725,738 [Application Number 08/600,636] was granted by the patent office on 1998-03-10 for method and apparatus for producing wood charcoal by pyrolysis of wood-like products or vegetable biomasses in general.
Invention is credited to Osvaldo Brioni, Dario Buizza.
United States Patent |
5,725,738 |
Brioni , et al. |
March 10, 1998 |
Method and apparatus for producing wood charcoal by pyrolysis of
wood-like products or vegetable biomasses in general
Abstract
A method and apparatus for producing wood charcoal by pyrolysis
of wood products or vegetable biomasses in general, the method
including the steps of: loading the wood products, or vegetable
biomasses in general, onto transport trolleys; introducing the
trolleys, which contain the wood products, in a treatment tunnel
wherein a pyrolysis chamber is formed; indirectly heating the wood
products inside the pyrolysis chamber until pyrolysis of the wood
products is obtained, with continuous extraction, from the
pyrolysis chamber, of the gas generated by the pyrolysis process;
and extracting the trolleys from the tunnel to unload from the
trolleys the charcoal that constitutes the residue of the pyrolysis
of the wood products.
Inventors: |
Brioni; Osvaldo (24030 Solza
(prov. of Bergamo), IT), Buizza; Dario (25035
Ospitaletto (prov. of Brescia), IT) |
Family
ID: |
11372506 |
Appl.
No.: |
08/600,636 |
Filed: |
February 13, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Nov 10, 1995 [IT] |
|
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MI95A2324 U |
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Current U.S.
Class: |
201/14; 201/32;
110/257; 202/117; 110/293 |
Current CPC
Class: |
C10B
53/02 (20130101); C10B 7/14 (20130101); Y02E
50/14 (20130101); Y02E 50/10 (20130101) |
Current International
Class: |
C10B
53/00 (20060101); C10B 53/02 (20060101); C10B
053/02 (); F23G 005/027 () |
Field of
Search: |
;201/13,32,14,15
;202/117 ;110/228,257,293,294 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wyse; Thomas G.
Claims
What is claimed is:
1. Method for producing wood charcoal by pyrolysis of wood
products, or vegetable biomasses in general, comprising the steps
of: loading the wood products onto transport trolleys; introducing
said trolleys, which contain the wood products, in a treatment
tunnel in which a pyrolysis chamber is formed; indirectly heating
the wood products inside said pyrolysis chamber until pyrolysis of
the wood products is obtained, with continuous extraction, from
said pyrolysis chamber, of the gas generated by the pyrolysis
process; and extracting the trolleys from said tunnel to unload
from the trolleys the charcoal that constitutes the residue of the
pyrolysis of the wood products.
2. Method according to claim 1, further comprising the step, prior
to the heating step, of drying and directly preheating the wood
products in said tunnel in a drying and preheating chamber located
upstream of said pyrolysis chamber relative to the advancement
direction of the trolleys along said tunnel.
3. Method according to claim 2, wherein during the drying and
preheating step the wood products are heated with a gas to a
temperature that is substantially between 120.degree. C. and
250.degree. C.
4. Method according to claim 1, wherein during said heating step
the wood products are heated to a temperature that is substantially
between 300.degree. C. and 600.degree. C.
5. Method according to claim 1, wherein during the heating step the
wood products are heated to a temperature that is substantially
between 400.degree. C. and 500.degree. C.
6. Method according to claim 1, further comprising the step, after
the heating step and prior to the extraction step, of cooling the
charcoal produced by the pyrolysis of the wood products in a
cooling chamber located in said tunnel downstream of said pyrolysis
chamber relative to the advancement direction of the trolleys along
said tunnel.
7. Method according to claim 6, wherein during the cooling step the
charcoal is brought to a temperature of less than 100.degree.
C.
8. Method according to claim 1, wherein the heating of the wood
products, during the heating step, is performed by means of
radiating bodies arranged in said pyrolysis chamber.
9. Method according to claim 8, wherein the gas extracted from said
pyrolysis chamber is used as fuel in a combustion chamber, the
fumes that leave said combustion chamber being fed into said
radiating bodies.
10. Method according to claim 9, wherein the fumes that leave said
radiating bodies are fed into said drying and preheating
chamber.
11. Method according to claim 10, wherein part of the gases that
leave said drying and preheating chamber is mixed with the fumes
that leave said radiating bodies prior to feeding them into said
drying and preheating chamber to adjust the temperature of the
fumes fed into said drying and preheating chamber.
12. Method according to claim 11, wherein part of the gases that
leave said drying and preheating chamber is mixed with the fumes
that leave said combustion chamber to adjust the temperature of the
fumes fed into said radiating bodies in the pyrolysis chamber.
13. Method according to claim 8, wherein the temperature of the
fumes fed into said radiating bodies is substantially 900.degree.
C.
14. Method according to claim 1, wherein part of the gas generated
by the pyrolysis process is subjected to separation of the
condensable part from the noncondensable part, said noncondensable
part being used as direct-cooling fluid and being fed into said
cooling chamber.
15. Method according to claim 14, wherein the tars produced by the
condensation of said condensable part are fed back into the
trolleys in said tunnel upstream of said pyrolysis chamber to be
redistilled.
16. Apparatus for producing vegetable charcoal by pyrolysis of wood
products, or vegetable biomasses in general, comprising: a
treatment tunnel; means for moving, along said tunnel, trolleys for
loading the wood products to be treated; means for separating the
inside of said tunnel from the outside environment; at least one
pyrolysis chamber being formed in said tunnel, said pyrolysis
chamber being provided with means for the indirect heating of the
wood products, which are introduced in said pyrolysis chamber, to a
temperature adapted to achieve the pyrolysis of said wood products;
and means for extracting from said pyrolysis chamber the gas
generated by the pyrolysis process.
17. Apparatus according to claim 16, wherein said tunnel lies on a
substantially horizontal plane and is substantially U-shaped, with
an inlet and an outlet that are arranged on a same side of the
tunnel.
18. Apparatus according to claim 16, wherein in said tunnel,
upstream of said pyrolysis chamber relative to the advancement
direction of said trolleys along said tunnel, a drying and
preheating chamber is provided that is separated from said
pyrolysis chamber and from the outside environment by at least one
door that is movable on command to allow the transit of the
trolleys.
19. Apparatus according to claim 16, wherein in said tunnel,
downstream of said pyrolysis chamber relative to the advancement
direction of said trolleys along said tunnel, a chamber for cooling
the charcoal produced by the pyrolysis of the wood products is
provided, said cooling chamber being separated from said pyrolysis
chamber and from the outside environment by at least one door that
is movable on command to allow the transit of the trolleys.
20. Apparatus according to claim 16, wherein said indirect heating
means comprise a battery of radiating bodies having a tubular
structure, located in said pyrolysis chamber, and connected to the
outlet of the fumes of at least one combustion chamber.
21. Apparatus according to claim 16, wherein said means for
extracting the gas generated by the pyrolysis process comprise an
extraction duct extending from said pyrolysis chamber and feeding a
burner of said combustion chamber.
22. Apparatus according to claim 20, wherein said radiating bodies
are connected to ducts for introducing the fumes into said drying
and preheating chamber.
23. Apparatus according to claim 16, further comprising a first
duct for collecting the drying gas and the vapor generated by the
wood products in said drying and preheating chamber, said first
duct for collecting the gas in said drying and preheating chamber
being connected, through an adjustment valve, to a duct for feeding
the fumes into said drying and preheating chamber, said duct being
connected to said radiating bodies to adjust the temperature of the
fumes fed into said drying and preheating chamber.
24. Apparatus according to claim 18, wherein at the inlet of said
drying and preheating chamber there is provided a compartment that
is separated from the remaining part of said drying and preheating
chamber by a movable door, another compartment being provided
proximate to the outlet of said cooling chamber and being separated
from the remaining part of said cooling chamber by a movable door,
said two compartments being kept at the equilibrium pressure by
aspirating exhaust gases from said two compartments and feeding
them therein.
25. Apparatus according to claim 24, further comprising a second
duct for collecting the gas arriving from said drying and
preheating chamber, said second duct for collecting the gas in said
drying and preheating chamber being connected, through an
adjustment valve, to the duct for the fumes that leave said
combustion chamber, which feeds said radiating bodies to adjust the
temperature of the fumes fed into said radiating bodies.
26. Apparatus according to claim 16, further comprising means for
separating the condensable component from the noncondensable
component of part of the gas produced by the pyrolysis of the wood
products in said pyrolysis chamber.
27. Apparatus according to claim 26, wherein said separation means
comprise at least one condenser cyclone the inlet whereof is
connected to said extraction duct.
28. Apparatus according to claim 27, wherein said condenser cyclone
is connected to said cooling chamber with one of its noncondensable
gas outlets.
29. Apparatus according to claim 28, further comprising a duct for
collecting the gas for cooling the charcoal in said cooling
chamber, said duct for collecting the gas in said cooling chamber
being connected to the inlet of said at least one condenser
cyclone.
30. Apparatus according to claim 16, further comprising an
additional combustion chamber with a burner that is supplied with
the gas, produced by the pyrolysis of the wood products, that is in
excess with respect to the energy required to make the pyrolysis
process self-sustaining.
31. Apparatus according to claim 30, further comprising a tank for
treating the condensable component of the gas produced by the
pyrolysis of the wood products.
32. Apparatus according to claim 31, further comprising a cyclone
chimney connected to the duct for discharging the fumes emitted by
said additional combustion chamber and to said second duct for
collecting the gas in said drying and preheating chamber to dispose
of the excess gases.
33. Apparatus according to claim 30, wherein said combustion
chamber is provided with a burner for startup and temperature
adjustment.
34. Apparatus according to claim 16, wherein said means for moving
said trolleys comprise a rail that runs along said tunnel and means
for the intermittent advancement of said trolleys along said tunnel
on said rail.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for
producing wood charcoal by pyrolysis of wood-like products or
vegetable biomasses in general.
Facilities of the "Lambiotte" type or the like are currently used
for producing, at the industrial level, wood charcoal starting from
wood products.
These facilities are generally constituted by a large cylindrical
retort made of metal plate, with a diameter that can vary between
1.75 and 3 meters and a height that can vary between 20 and 22
meters. The wood products are loaded at the upper end of the
cylindrical retort and are heated by the fumes of an external
furnace, which enter the cylindrical retort in an intermediate
region of its vertical extension. The mixture of distillation
products and fumes exits from the retort proximate to the upper end
and is sent to appropriate condensation systems, where the
condensable vapors are separated from the non-condensable gases
which, at the output of the condensation system, are sent back to
the external furnace so that they can be reused to provide energy
to support the process.
The lowermost part of the cylindrical retort constitutes the
charcoal cooling region; said charcoal is dropped intermittently
into trolleys that pass below the cylindrical retort.
The operation of these facilities is continuous with wood products
formed by cylindrical pieces having a diameter of 8-12 cm or a side
dimension of 15 to 20 cm; with facilities using a cylindrical
retort measuring 1.75 m in diameter, it is possible to produce
approximately 300 quintals of charcoal per day, keeping the wood
products inside the retort for approximately 12 hours.
These facilities, however, are not free from problems and
drawbacks.
These problems arise mainly from the fact that these facilities,
like other conventional facilities, follow a carbonization method
that utilizes the principle of partial combustion of the wood
products in vertical retorts, consequently penalizing the
efficiency of the facility.
Furthermore, for correct operation of these facilities, the wood
that is introduced must have specific geometrical features, such as
to facilitate its descent inside the retort, and a very low
moisture content to allow its carbonization. Accordingly, these
requirements force expensive processing of the raw material to
reduce it into small pieces and the adoption of an additional
drying oven to reduce the moisture to the levels that are
indispensable for executing the process. Analysis of the facilities
and processes currently being used to produce charcoal starting
from wood products has pointed out the following limitations: high
specific consumption of wood per unit of charcoal obtained;
low production capacity, caused by the size limitations of
continuous vertical ovens;
expensive processing of the wood to reduce it to the physical
conditions required by the process (size and humidity);
low overall thermal efficiency, linked to carbonization with direct
heat generated by the partial combustion of the wood and of its
organic emissions, a considerable part whereof is eliminated
uselessly;
poor operating flexibility as regards the carbonization process
parameters;
considerable ecologic problems, caused by the volatile pyroligneous
products and by the large amount of charcoal dust generated;
difficult maintenance, caused by the considerable height of the
installations;
high consumptions of electric power for the pretreatment of the
wood and subsequently for its vertical transport in the drying and
carbonization ovens;
very high specific investment per unit of product; and
low flame temperatures (700.degree.-800.degree. C.) during
combustion of the pyrolytic products. Accordingly, thermal
applications such as the production of electric power, "cracking"
of pyrolytic products, etcetera, become more difficult.
SUMMARY OF THE INVENTION
A principal aim of the present invention is to solve the problems
described above by providing a method for producing wood charcoal
by pyrolysis of wood products, or vegetable biomasses in general,
that is capable of sustaining itself energywise and avoids even
partial combustion of the raw material.
Another aim of the invention is to provide a method that
considerably simplifies, with respect to conventional charcoal
production processes, the operations for energy recovery and
optionally for purifying the gases released by the wood products
during pyrolysis.
Another aim of the invention is to provide a method having a high
overall thermal efficiency.
Another aim of the invention is to provide an apparatus that allows
to produce charcoal starting from wood products, even considerably
large ones, without having to resort to expensive operations for
pretreating the wood products.
Another aim of the invention is to provide a facility that can be
produced and installed, as well as subjected to maintenance
interventions, in an extremely simpler and quicker manner than
conventional charcoal production apparatuses.
Another aim of the invention is to provide a method and an
apparatus that allow to produce wood charcoal with an extremely low
emission of pollutants into the atmosphere and in any case at such
levels as to be considerably lower than the limits prescribed by
applicable statutory provisions for environmental protection.
According to one preferred aspect of the invention, there is
provided a method for producing wood charcoal by pyrolysis of wood
products, or vegetable biomasses in general, characterized in that
it comprises: a step for loading the wood products onto transport
trolleys; a step for introducing said trolleys, which contain the
wood products, into a treatment tunnel wherein a pyrolysis chamber
is formed; a step for the indirect heating of the wood products
inside said pyrolysis chamber until pyrolysis of the wood products
is obtained, with continuous extraction, from said pyrolysis
chamber, of the gas generated by the pyrolysis process; and a step
for the extraction of the trolleys from said tunnel to unload from
the trolleys the charcoal that constitutes the residue of the
pyrolysis of the wood products.
The execution of the method according to the invention preferably
utilizes an apparatus comprising: a treatment tunnel; means for
moving, along said tunnel, the trolleys for loading the wood
products to be treated; means for separating the inside of said
tunnel from the outside environment; at least one pyrolysis chamber
being formed in said tunnel and being provided with means for the
indirect heating of the wood products introduced in said pyrolysis
chamber to a temperature adapted to achieve pyrolysis of the wood
products; and means for extracting the gas generated by the
pyrolysis process from said pyrolysis chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
The characteristics and advantages of the invention will become
apparent from the following detailed description of some preferred
but not exclusive embodiments of the method and apparatus according
to the invention, described and illustrated in the accompanying
drawings only by way of non-limitative example, wherein:
FIG. 1 is a diagram of an apparatus for producing wood charcoal
according to a preferred embodiment of the invention;
FIG. 2 is a schematic view of means for moving the wood product
loading trolleys along the treatment tunnel;
FIG. 3 is a schematic sectional view of the pyrolysis chamber,
taken along a vertical plane;
FIG. 4 is a general flowchart of a method for producing wood
charcoal according to a preferred aspect of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to the above figures, an apparatus for producing
wood charcoal, generally designated by the reference numeral 1,
comprises a treatment tunnel 2 lying preferably on a horizontally
plane and in a substantially U-shaped arrangement, so as to have an
inlet 3 and an outlet 4 that are arranged on a same side.
The apparatus comprises means for moving trolleys 5 along the
tunnel 2; the wood products to be treated are loaded into said
trolleys.
The means for moving the trolleys 5 inside the tunnel 2 preferably
comprise rails 6, which run axially along the two arms 2a and 2b of
the tunnel 2, and a beam 7a and 7b for each one of the two arms of
the tunnel 2; each beam is slidingly accommodated in a respective
seat 8 extending along the bottom of the tunnel between the rails
6.
Each beam 7a and 7b is slidably actuatable with a reciprocating
motion, for example by means of fluid-actuated cylinders 9a and 9b
that are actuatable on command, parallel to the extension of the
corresponding arm of the tunnel 2 in which it is accommodated.
Moreover, each beam 7a and 7b is provided with sets of locators or
pushers 10a and 10b that can be extracted on command in an upward
direction from the beam 7a and 7b, for example by means of
fluid-actuated cylinders 11a, 11b, 12a, 12b, to be engaged or
disengaged with respect to the trolleys 5 arranged on the rails
6.
In practice, the advancement of the trolleys 5 along the tunnel 2
is performed in an intermittent fashion through the combined
actuation of the fluid-actuated cylinders 9a and 9b, which cause
the reciprocating motion of the beams 7a and 7b along the tunnel,
and of the fluid-actuated cylinders 11a, 11b, 12a, 12b, which
engage and disengage the locators 10a and 10b with the trolleys,
transmitting the translatory motion of the beam to the
trolleys.
A device for transferring the trolleys from the rails arranged
along the arm 2a of the tunnel to the rails arranged on the arm 2b
is provided along the transverse portion 2c that joins the two
parallel arms 2a and 2b of the tunnel 2, said device being
constituted for example by a movable platform 13 for supporting the
trolleys.
The transfer of the movable platform 13 from one arm of the tunnel
to the other can be achieved for example by means of a
fluid-actuated cylinder 14 acting on the movable platform 13,
causing its reciprocating movement along a direction lying at right
angles to the main dimension of the two parallel arms 2a and 2b of
the tunnel 2.
A drying and preheating chamber 20, a pyrolysis chamber 21, and a
cooling chamber 22 are formed in the tunnel 2 starting from the
inlet 3 and along the direction 100 in which the trolleys 5 advance
along the tunnel 2; said pyrolysis chamber is divided into a first
section, located in the arm 2a of the tunnel, and into a second
section, located in the arm 2b of the tunnel.
A plurality of guillotine doors are preferably provided between the
inlet 3 and the pyrolysis chamber 21, so that during the operation
of the apparatus any direct connection of the pyrolysis chamber 21
to the outside is safely prevented.
Preferably, at the inlet of the drying and preheating chamber 20
there is a first compartment 24 for containing a trolley 5 and
separated from the outside environment and from the remaining part
of the chamber 20 by two guillotine doors 25 and 26 that are opened
and closed for example through fluid-actuated cylinders 27 and
28.
At the end of the drying and preheating chamber 20 a second
compartment 29 is provided which has the same dimensions as the
compartment 24 and is separated from the remaining part of the
chamber 20 and from the pyrolysis chamber 21 by guillotine doors 30
and 31, the opening whereof is actuated by fluid-actuated cylinders
32 and 33, like the guillotine doors 25 and 26.
At the exit of the pyrolysis chamber 21, that is to say, at the
beginning of the cooling chamber 22, a third compartment 34 is
advantageously provided which has the same dimensions as the
compartments 24 and 29 and is separated from the remaining part of
the cooling chamber 22 and from the pyrolysis chamber 21 by
guillotine doors 35 and 36 that are actuated by fluid-actuated
cylinders 37 and 38.
Likewise, at the end of the cooling chamber 22 a fourth compartment
39 is conveniently provided which is separated from the outside
environment and from the remaining part of the cooling chamber 22
by guillotine doors 40 and 41 that are actuated by fluid-actuated
cylinders 42 and 43.
At least two sets of locators or pushers 10a and 10b are provided
along each arm of the tunnel 2, on the beam 7a or 7b, and are
actuatable independently from one another by virtue of the
fluid-actuated cylinders 11a, 12a, 11b, and 12b, so that the
insertion of a trolley 5 in the inlet 3 of the tunnel occurs when
the doors 25 and 31 are open and the doors 26 and 30 are closed,
whereas the passage of the trolley from the first compartment 24
into the drying and preheating chamber 20, as well as the passage
of the trolley into the second compartment 29, are performed when
the doors 26 and 30 are open, after the closure of the doors 25 and
31. The same arrangement is provided on the other arm of the
tunnel, so that the pyrolysis chamber 21 can never be directly
connected to the adjacent environment. By virtue of this
arrangement, combined with the presence of the compartments 24, 29,
34, and 39, the emission of pollutants into the outside environment
is practically eliminated. Furthermore, the various regions into
which the tunnel 2 is divided are never simultaneously connected to
each other during the operation of the apparatus.
For the sake of greater clarity, the doors that separate the
various chambers formed in the tunnel 2, as well as the beams 7a
and 7b with the corresponding locators 10a and 10b, have been shown
on a plane that is rotated through 90.degree. with respect to the
actual plane of arrangement relative to the tunnel in FIG. 2.
Furthermore, the beams 7a and 7b, as well as the locators 10a and
10b and the corresponding actuation elements, have been shown
laterally adjacent to the two arms 2a and 2b of the tunnel shown in
plan view.
Proximate to the inlet 3 and to the outlet 4 of the tunnel there is
provided a device for transferring the trolleys 5 from the outlet
towards the inlet; said transfer device is constituted for example
by a movable platform 45 for supporting the trolleys that is
actuated by a fluid-actuated cylinder 46.
The entire system for moving the trolleys and the doors is
controlled by a control and monitoring element, for example a PLC,
that supervises the movement of said elements according to a
programmed sequence.
The apparatus according to the invention, in a preferred
embodiment, is provided, inside the pyrolysis chamber 21, with
means for the indirect heating of the wood products contained in
the trolleys 5. Said indirect heating means are preferably
constituted by radiating bodies 50, such as for example batteries
of tubular bodies, which are supplied, through a duct 51, with the
fumes of a combustion chamber 52.
The radiating bodies 50, at the exit of the pyrolysis chamber 21,
are connected to a duct 53 provided with outlets arranged in the
drying and preheating chamber 20. An aspirator 54 is arranged along
the duct 53 and maintains the necessary flow of the fumes arriving
from the combustion chamber 52 through the radiating bodies 50 and
conveys the fumes, after passing through the radiating bodies 50,
into the drying and preheating chamber 20. A first duct 55 is
provided along the longitudinal extension of the drying and
preheating chamber 20, and part of the gas, constituted by said
fumes and by the water vapor generated by the heating of the wood
products in the drying and preheating chamber 20, is conveyed
through said duct 55 into the duct 53 and is then fed back into the
drying and preheating chamber 20. An aspirator 56 is arranged along
the duct 55, and the feeding of the gases arriving from the drying
and preheating chamber 20 into the duct 53 is adjustable by means
of a valve 57 so as to allow adjustment of the temperature of the
fumes that are introduced in the drying and preheating chamber 20
through the duct 53 to avoid the combustion of the wood
products.
A second duct 58 is provided along the longitudinal extension of
the drying and preheating chamber 20 and is connected to the duct
51.
More particularly, an aspirator 59 and a valve 60 are arranged
along the duct 58; by virtue of said valve, it is possible to
adjust the flow-rate of the gases that are removed from the drying
and preheating chamber 20 through the duct 58 and are, if
necessary, partially fed into the duct 51, so as to allow to adjust
the temperature of the fumes that arrive from the combustion
chamber 52 and are fed into the radiating bodies 50; the excess
part of the gases arriving from the duct 58 is sent to a cyclone
chimney 76.
The apparatus according to a preferred aspect of the invention
comprises means for extracting the gas generated by the pyrolysis
process; said means are preferably substantially constituted by an
extraction duct 61 provided with a plurality of inlets arranged in
various regions of the pyrolysis chamber 21 and feeding the burner
62 arranged in the combustion chamber 52.
Along the extension of the duct 61 a branch 61a is provided,
through which part of the gases arriving from the pyrolysis chamber
21 is optionally conveyed to a battery of condenser cyclones,
designated by the reference numerals 63 to 66; the condensation
produces a noncondensable gas, with a low oxygen content, that
supplements any losses of the cooling gas.
The condenser cyclones 63-66 are connected to each other in series,
so as to perform a gradual reduction of the temperature and
therefore separate the condensable part from the noncondensable
part of a partial amount of the gases produced by pyrolysis of the
wood products.
The condensable part of said gases is recovered in a collection
tank 67, whereas the cooled noncondensable part exits from the last
condenser cyclone 66 through a duct. 68, along which an aspirator
69 is provided that ensures the gas flow along the ducts 61 and 61a
and conveys the noncondensable part, through branches of said duct
68, into the cooling chamber 22, in order to provide a stream of
cooling gas that strikes the charcoal inside the trolleys in the
cooling chamber 22.
The inlets of branches of a charcoal cooling gas collection duct 71
are located in the initial part of the cooling chamber 22; said
duct 71 is connected to one of the inlets of the condenser cyclone
64.
It should be noted that in the cooling chamber 22 it is possible to
provide cooling water sprayers 72 that can be supplied with the
water taken from the tank 67.
The cooling water used for the condenser cyclones is in turn cooled
by means of a set of air coolers 81.
Any tars collected in the portion 67a of the tank 67 can be
separated and used, or can be fed back into the trolleys inside the
tunnel 2, upstream of the pyrolysis chamber 21, through the pump 82
and the pipe 83 to be distilled again.
The cooling gas, to be conveyed into the cooling chamber 22, can
also be obtained by using burnt gas generated within the process,
such as for example the gas that leaves the radiating bodies,
brought to the desired temperature by introducing micronized water
into the extraction duct. The introduction of micronized water also
reduces the oxygen content of said gas to less than 6%, making it
practically inert.
The pressure inside the tunnel 2 is slightly higher than the
pressure of the outside environment. The first compartment 24 and
the last compartment 39 are kept at the equilibrium pressure, so as
to avoid the escape of polluting gases and vapors, by virtue of the
aspiration and feeding of exhaust gases through the pipes 70 and 79
controlled by the fan 56 and by the valves 80a and 80b.
The apparatus according to a preferred embodiment of the invention
furthermore comprises an additional combustion chamber 73, wherein
the gases produced by the pyrolysis of the wood products in the
pyrolysis chamber 21 are subjected to combustion; said gases would
be in excess with respect to the energy required to make the entire
process self-sustaining. The fumes produced by the additional
combustion chamber 73 can be used, for example, to heat water for
hydraulic or sanitary uses, to generate electricity, or for other
uses.
The discharge 74 of the additional combustion chamber 73, along
which an aspirator 75 is arranged, is connected to the cyclone
chimney 76.
The duct 58 for discharging the part of gas arriving from the
drying and preheating chamber 20 in excess with respect to the
demand for adjusting the temperature of the fumes introduced in the
radiating bodies 50 is also connected to the cyclone chimney 76
through an additional duct 77 and a valve 78.
For the sake of completeness in description, it should be noted
that the apparatus includes an additional tank 77a for collecting
meteoric water, as well as for supplying the condenser cyclones
63-66.
The operation of the preferred embodiment of the apparatus, and a
preferred method, according to the invention are as follows.
The trolleys 5, loaded with the wood products to be carbonized, are
introduced in the tunnel 2 and moved intermittently forwards along
the longitudinal extension of the tunnel 2.
During advancement inside the tunnel, the trolleys 5 pass initially
into the first compartment 24 and then, in the manner provided to
minimize connection of the inside of the tunnel to the outside,
along the drying and preheating chamber 20. The introduction inside
the drying and preheating chamber 20 of the fumes arriving from the
radiating bodies 50 through the duct 53 ensures that a temperature
substantially between 120.degree. C. and 250.degree. C. is
maintained inside the drying and preheating chamber. A
substantially complete drying of the wood products and their
preheating are achieved at this temperature. The drying and
preheating of the wood products generate a gas that is constituted
substantially entirely by water vapor, and is used, mixed with the
exhaust fumes of the exchangers, as already explained, to adjust
the temperature of the fumes arriving from the radiating bodies 50
prior to their introduction in the drying and preheating chamber
20. Another part of this gas is extracted through the duct 58 and
used to adjust the temperature of the fumes arriving from the
combustion chamber 52 before they are fed into the radiating bodies
50.
This adjustment is performed so that the fumes at the inlet of the
radiating bodies 50 have a temperature of approximately 900.degree.
C., so as to maintain, inside the pyrolysis chamber 21, a
temperature that is preferably substantially between 300.degree. C.
and 600.degree. C., most preferably between 400.degree. C. and
500.degree. C.
After the drying and preheating chamber 20, the wood products are
fed, by virtue of the intermittent advancement of the trolleys 5 in
the tunnel 2, into the pyrolysis chamber 21, where the wood
products contained in the trolleys 5 are heated indirectly,
achieving their pyrolysis, i.e., the thermochemical decomposition
of the organic matter constituting the wood products. The products
of this thermochemical reaction, which occurs practically in the
absence of air, are constituted by the charcoal that remains in the
trolleys 5 and by a gaseous phase that is removed from the
pyrolysis chamber 21 through the duct 61. The gaseous phase is in
turn formed by a condensable component and by a noncondensable
component.
The condensable component substantially contains water, tars,
pitches, aliphatic and/or aromatic hydrocarbons, organic acids,
alcohols, ketones, aldehydes, and the noncondensable phase
substantially contains hydrogen, light hydrocarbons, carbon
monoxide, and carbon dioxide.
The gaseous phase is sent, through the duct 61, directly to the
combustion chamber 52 and, if an excess of this gaseous phase with
respect to the self-sustenance requirements of the process occurs,
the excess part is burned in the additional combustion chamber
73.
As already explained, part of the gaseous phase taken from the
pyrolysis chamber 21 is conveyed, through the duct 61a, to the
battery of condenser cyclones 63-66, where the condensable
component is separated from the noncondensable component.
The condensable component is collected in the tank 67, whereas the
noncondensable component is conveyed through the duct 68 into the
cooling chamber 22.
After a retention time allowing complete pyrolysis of the wood
products, the trolleys 5 carry the wood products into the cooling
chamber 22, where the introduction of the cooled noncondensable
component and the optional spraying of water through the sprayers
72 lowers the temperature of the charcoal below 100.degree. C., so
as to safely avoid any spontaneous combustion of the charcoal when
exiting from the tunnel.
Finally, the trolleys with the charcoal produced by the pyrolysis
of the wood products are removed from the tunnel, emptied of the
charcoal, repositioned at the inlet of the tunnel 2, and then
filled with fresh wood products to be carbonized. It should be
noted that although the advancement of the trolleys 5 inside the
tunnel 2 is intermittent, the charcoal production process is
practically continuous.
In practice the preferred method is self-sustained energywise,
since the energy required to achieve pyrolysis of the wood products
is produced by the combustion of the gases generated from the
pyrolysis process.
The only additional energy input is constituted by an auxiliary
supply provided in the combustion chamber 52 with external fuel,
constituted for example by methane, to start the apparatus and to
adjust the temperature of the fumes produced.
The retention time of each trolley inside the tunnel 2 varies as a
function of the moisture, size, and type of the wood products
subjected to pyrolysis. All the process parameters, temperatures,
and pressures, are controlled by an automatic regulation
system.
In practice it has been observed that the preferred method and
apparatus according to the invention advantageously allow to
produce charcoal with practically no consumption of the wood
products and therefore with high efficiency.
The sensible heat of the fumes that is transmitted to the raw
material, both by direct contact in the drying and preheating
chamber, and indirectly by means of the radiating exchangers in the
pyrolysis chamber, effectively avoids the mixing of the gases
produced by wood pyrolysis, preventing water, carbon dioxide, and
nitrogen from reducing the heat value thereof and preventing oxygen
from contributing to their combustion. Accordingly, optimum thermal
efficiency, high productivity of wood charcoal, and overall
recovery of concentrated pyroligneous products are achieved.
Although the preferred method and apparatus according to the
invention have been studied particularly for the production of
charcoal by using wood products as raw material, they can in any
case be used to produce charcoal starting from vegetable biomasses
in general.
The preferred method and apparatus thus conceived are susceptible
of numerous modifications and variations, all of which are within
the scope of the inventive concept; all the details may furthermore
be replaced with other technically equivalent elements.
In practice, the materials employed, as well as the dimensions, may
be any according to the requirements and the state of the art.
* * * * *